The present invention relates generally to the attachment of pipes and thermoplastic fitting components by means of fusion welding. More particularly, the invention relates to improved fittings for joining thermoplastic components.
A number of companies have developed plastic welding equipment which utilizes specialized fitting components to join thermoplastic piping. Plastic welding can be categorized into three types: fusion welding, IR Butt Fusion, and Bead and Crevice Free welding. Fusion welding is used for high purity installations of thermoplastic piping. Thermoplastic piping has grown in industrial usage because of its compatibility with chemicals, its non-corrosive nature, ease of installation, long life, and its smooth internal surfaces. These features of thermoplastic piping make it ideal for high purity applications.
Standard fusion welding involves the heat fusion of a pipe into a female socket fitting. Bonding is achieved by heating the mating surfaces of the pipe end and of the fitting to a temperature above the melt point of the material. The heated parts are then engaged and held together until fused. Fusion occurs when the parts are cooled to below the melt point of the material.
Heating is typically achieved through conductive means via an electric heater that reaches temperatures in the regions of 500° F.±10° (or 260° C.). With the appropriate time, the pipe and fitting surfaces which come in direct contact with the heating tool will melt. The parts are then carefully removed from the heating tool and quickly pushed together thereby fusing the two parts together. Fusion welding is also used for welding a pipe or fitting to a plate in the same manner described above except the plate replaces the female socket.
The relationship between the outside diameter of the pipe and the bore of the fitting or plate is critical for successful fusion welding. Interference is essential when the hot surfaces are mated together. A carefully designed interference fit of the heated mating parts provides consistency of joining. It also results in the appearance of a weld bead as excess melted material is “scraped” off one of the surfaces. This weld bead is undesirable to some users because of its fabricated, unfinished look; and because of the potential for the weld to entrap airborne particles that can be embedded in the material while in a melted state.
The weld bead provides insight to whether the heat fusion joint was properly made. Ideally a double weld should be present and it should not be large in size. As stated above, one disadvantage to the weld bead is that it gives the joint a fabricated appearance. Another disadvantage is that dark spots may appear on the areas of the weld bead due to normal heating or particles which may have been captured when the material was in a melted state. Some manufacturers that use heat fusion to produce products machine the weld bead in order to create a more professional molded look. This adds an additional step to the manufacturing process.
Accordingly, there is a need for an improved fitting that integrates the weld bead into the fitting resulting in the final product having a more finished look. Additionally, an improved fitting that will prevent the common mistake of over inserting a mated component by providing an additional stop to the fitting is needed. Moreover, there is a need for reducing the manufacturing steps involved in heat fusion by eliminating removal of the weld bead through machining. The present invention fulfills these needs and provides other related advantages.